Excitation Synthesis

For a further reduction in cost of implementation, particularly with
respect to memory usage, it is possible to synthesize the
excitation using a noisesignal through a time-varying lowpass filter
[443]. The synthesis replaces the recorded
soundboard/enclosure sound. It turns out that the sound produced by
tapping on a piano soundboard sounds very similar to noise which is
lowpass-filtered such that the filter bandwidth contracts over time.
This approach is especially effective when applied only to the
high-frequency residual excitation after factoring out all
long-ringing modes as biquads.